The orientation of various membrane-bound paramagnetic biological molecules will be determined by esr spectroscopy. Multilayers of the membrane containing the paramagnetic species will be produced on quartz slides by air drying of the membrane suspension. By recording the esr spectrum of these molecules as a function of the angle subtended by the multilayer and the spectrometers magnetic field, the orientation of the molecule in the membrane can be deduced. Systems to be studied will be Signal II and membrane-bound Mn2 ion in chloroplasts as well as nitrogenase in Azotobaster vinelandii.